ESM Support

To use ts-jest with ESM support:

• Check ESM Jest documentation.
• Enable useESM true for ts-jest config.
• Include .ts in extensionsToTreatAsEsm Jest config option.
• Ensure that tsconfig has module with value for ESM, e.g. ES2015 or ES2020 etc...

ESM presets

There are also 3 presets to work with ESM.

caution

If you are using custom transform config, please remove preset from your Jest config to avoid issues that Jest doesn't transform files correctly.

Examples

Manual configuration

JavaScript

// jest.config.js
/** @type {import('ts-jest').JestConfigWithTsJest} */
module.exports = {
  // [...]
  extensionsToTreatAsEsm: ['.ts'],
  moduleNameMapper: {
    '^(\\.{1,2}/.*)\\.js$': '$1',
  },
  transform: {
    // '^.+\\.[tj]sx?$' to process ts,js,tsx,jsx with `ts-jest`
    // '^.+\\.m?[tj]sx?$' to process ts,js,tsx,jsx,mts,mjs,mtsx,mjsx with `ts-jest`
    '^.+\\.tsx?$': [
      'ts-jest',
      {
        useESM: true,
      },
    ],
  },
}

TypeScript

// jest.config.ts
import type { JestConfigWithTsJest } from 'ts-jest'

const jestConfig: JestConfigWithTsJest = {
  // [...]
  extensionsToTreatAsEsm: ['.ts'],
  moduleNameMapper: {
    '^(\\.{1,2}/.*)\\.js$': '$1',
  },
  transform: {
    // '^.+\\.[tj]sx?$' to process ts,js,tsx,jsx with `ts-jest`
    // '^.+\\.m?[tj]sx?$' to process ts,js,tsx,jsx,mts,mjs,mtsx,mjsx with `ts-jest`
    '^.+\\.tsx?$': [
      'ts-jest',
      {
        useESM: true,
      },
    ],
  },
}

export default jestConfig

JSON

// package.json
{
  // [...]
  "jest": {
    "extensionsToTreatAsEsm": [".ts"],
    "moduleNameMapper": {
      "^(\\.{1,2}/.*)\\.js$": "$1"
    },
    "transform": {
      // '^.+\\.[tj]sx?$' to process ts,js,tsx,jsx with `ts-jest`
      // '^.+\\.m?[tj]sx?$' to process ts,js,tsx,jsx,mts,mjs,mtsx,mjsx with `ts-jest`
      "^.+\\.tsx?$": [
        "ts-jest",
        {
          "useESM": true
        }
      ]
    }
  }
}

Use ESM presets

important

Starting from v28.0.0, ts-jest will gradually switch to esbuild/swc to transform ts to js. To make the transition smoothly, we introduce legacy presets as a fallback when the new codes don't work yet.

JavaScript

// jest.config.js
/** @type {import('ts-jest').JestConfigWithTsJest} */
module.exports = {
  // [...]
  preset: 'ts-jest/presets/default-esm', // or other ESM presets
  moduleNameMapper: {
    '^(\\.{1,2}/.*)\\.js$': '$1',
  },
  transform: {
    // '^.+\\.[tj]sx?$' to process ts,js,tsx,jsx with `ts-jest`
    // '^.+\\.m?[tj]sx?$' to process ts,js,tsx,jsx,mts,mjs,mtsx,mjsx with `ts-jest`
    '^.+\\.tsx?$': [
      'ts-jest',
      {
        useESM: true,
      },
    ],
  },
}

TypeScript

// jest.config.ts
import type { JestConfigWithTsJest } from 'ts-jest'

const jestConfig: JestConfigWithTsJest = {
  // [...]
  preset: 'ts-jest/presets/default-esm', // or other ESM presets
  moduleNameMapper: {
    '^(\\.{1,2}/.*)\\.js$': '$1',
  },
  transform: {
    // '^.+\\.[tj]sx?$' to process ts,js,tsx,jsx with `ts-jest`
    // '^.+\\.m?[tj]sx?$' to process ts,js,tsx,jsx,mts,mjs,mtsx,mjsx with `ts-jest`
    '^.+\\.tsx?$': [
      'ts-jest',
      {
        useESM: true,
      },
    ],
  },
}

export default jestConfig

JSON

// package.json
{
  // [...]
  "jest": {
    "preset": "ts-jest/presets/default-esm", // or other ESM presets,
    "moduleNameMapper": {
      "^(\\.{1,2}/.*)\\.js$": "$1"
    },
    "transform": {
      // '^.+\\.[tj]sx?$' to process ts,js,tsx,jsx with `ts-jest`
      // '^.+\\.m?[tj]sx?$' to process ts,js,tsx,jsx,mts,mjs,mtsx,mjsx with `ts-jest`
      "^.+\\.tsx?$": [
        "ts-jest",
        {
          "useESM": true
        }
      ]
    }
  }
}

Support .mts extension

To work with .mts extension, besides the requirement to run Jest and ts-jest in ESM mode, there are a few extra requirements to be met:

• package.json should contain "type": "module"
• A custom Jest resolver to resolve .mjs extension, see our simple one at https://github.com/kulshekhar/ts-jest/blob/main/e2e/native-esm-ts/mjs-resolver.ts
• tsconfig.json should at least contain these following options

// tsconfig.spec.json
{
  "compilerOptions": {
    "module": "Node16", // or "NodeNext"
    "target": "ESNext",
    "moduleResolution": "Node16", // or "NodeNext"
    "esModuleInterop": true
  }
}